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United States Patent |
6,040,887
|
Matsuyama
,   et al.
|
March 21, 2000
|
Liquid crystal display device with wide viewing angle characteristics
comprising high resistivity black matrix
Abstract
A liquid crystal display device comprising a black mask formed on one of a
pair of substrates at least one of which is transparent, a group of
electrodes formed on at least one of the pair of substrates, a liquid
crystal layer comprising a liquid crystal composition substance having a
dielectric anisotropy and held between the pair of substrates, an
orientation control film formed between the liquid crystal layer and one
of the substrates for orienting liquid crystal molecules of the liquid
crystal composition substance in a predetermined direction, a polarizer
laminated on at least one of the pair of substrates, and a driver for
applying a drive voltage to the group of electrodes, wherein the group of
electrodes has a structure that the electrodes are so arranged as to
generate an electric field having a component predominantly in parallel
with the interface between the orientation control film and the liquid
crystal layer, the liquid crystal composition substance has a resistivity
of not smaller than 10.sup.N .OMEGA..multidot.cm, and the black mask has a
resistivity of not smaller than 10.sup.M .OMEGA..multidot.cm, wherein N
and M are integers satisfying the relationships N.gtoreq.9 and M.gtoreq.6.
Inventors:
|
Matsuyama; Shigeru (Mobara, JP);
Asuma; Hiroaki (Mobara, JP);
Shimura; Masato (Mobara, JP);
Tomita; Yoshifumi (Mobara, JP);
Aratani; Sukekazu (Hitachi, JP)
|
Assignee:
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Hitachi, Ltd. (Tokyo, JP)
|
Appl. No.:
|
181039 |
Filed:
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October 28, 1998 |
Foreign Application Priority Data
| Jun 14, 1995[JP] | 7-147720 |
| Jul 27, 1995[JP] | 7-191994 |
| Jul 27, 1995[JP] | 7-192004 |
Current U.S. Class: |
349/141; 349/44; 349/110; 349/143 |
Intern'l Class: |
G02F 001/133.5; G02F 001/139.3; G02F 001/136 |
Field of Search: |
349/110,111,44,141,143
430/7
|
References Cited
U.S. Patent Documents
4308319 | Dec., 1981 | Michelotti et al. | 428/432.
|
5117299 | May., 1992 | Kondo et al. | 349/141.
|
5412494 | May., 1995 | Ishiwata et al. | 349/111.
|
5558927 | Sep., 1996 | Aruga et al. | 430/70.
|
5598285 | Jan., 1997 | Kondo et al. | 349/42.
|
Other References
"Electrical Characteristics of Black Matrix for Super-TFT-LCDs", H. Asuma,
et al., International Display Workshops, Nov. 1997, pp. 167-170.
|
Primary Examiner: Sikes; William L.
Assistant Examiner: Ton; Toan
Attorney, Agent or Firm: Antonelli, Terry, Stout & Kraus, LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This is a continuation of U.S. application Ser. No. 08/659,650, filed Jun.
6, 1996, U.S. Pat. No. 5,831,701 the subject matter of which is
incorporated by reference herein.
Claims
What is claimed is:
1. A liquid crystal display device comprising:
a pair of substrates at least one of which is transparent;
a black mask formed on one of said pair of substrates and having an opening
which has at least one pair of edges confronting each other and extending
in a first direction;
a first group of electrodes and a second group of electrodes being formed
on at least one of said pair of substrates, extending in the first
direction of said one pair of edges of said opening of said black mask and
one of said first group of electrodes being disposed alternately with one
of said second group of electrodes;
a liquid crystal layer comprising a liquid crystal composition substance
having a dielectric anisotropy and held between said pair of substrates;
an orientation control film formed between said liquid crystal layer and
one of said pair of substrates for orienting liquid crystal molecules of
said liquid crystal composition substance in a predetermined direction;
a polarizing means laminated on at least one of said pair of substrates;
and
a drive means for applying a drive voltage to at least one of said first
group of electrodes and said second group of electrodes;
at least one of said first group of electrodes and at least one of said
second group of electrodes are spaced from each other so as to divide a
region enclosed by said opening of said black mask into a pair of first
regions and at least one second region and to generate an electric field
having a component predominantly in parallel with the interface between
said orientation control film and said liquid crystal layer in each of
said pair of first regions and said at least one second region, said pair
of first regions and said at least one second region extending in the
first direction of said one pair of edges of said opening of said black
mask;
one of said pair of first regions being disposed adjacent to one of said
one pair of edges of said opening of said black mask and another of said
pair of first regions being disposed adjacent to another of said one pair
of edges of said opening of said black mask;
said at least one second region being spaced from both of said one pair of
edges of said opening of said black mask by each of said of first regions,
respectively,
said liquid crystal composition substance has a resistivity of not smaller
than 10.sup.N .OMEGA..multidot.cm, and
said black mask has a resistivity of not smaller than 10.sup.M
.OMEGA..multidot.cm,
wherein N and M are integers satisfying the relationships N.gtoreq.9 and
M.gtoreq.6.
2. A liquid crystal display device according to claim 1, wherein metal
oxide particles are contained in said black matrix.
3. A liquid crystal display device according to claim 2, wherein said metal
oxide particles are particles of at least one cobalt oxide, chromium
oxide, manganese oxide and nickel oxide.
4. A liquid crystal display device according to claim 2, wherein either or
both of an organic pigment and a graphite powder in addition to said metal
oxide particles are contained in said black mask.
5. A liquid crystal display device according to claim 3, wherein said
cobalt oxide particles are chiefly tricobalt tetroxide particles.
6. A liquid crystal display device according to claim 3, wherein any one of
chromium oxide, manganese oxide and nickel oxide is contained in addition
to said cobalt oxide.
7. A liquid crystal display device according to claim 1, wherein the base
material of said black mask is made of a polyimide resin.
8. A liquid crystal display device according to claim 7, wherein the
composition of said polyimide resin material contains a component that is
cured by light and a component that is cured by heat, and the optical
density of said black mask increases as said resin material is cured by
heat.
9. A liquid crystal display device according to claim 7, wherein said black
mask is composed of a polyimide resin material which contains at least one
or more kinds of black coloring agents and other coloring agents different
from said black coloring agents.
10. A liquid crystal display device according to claim 8, wherein said
black mask is composed of a polyimide resin material which contains at
least one or more kinds of black coloring agents and other coloring agents
different from said black coloring agents.
11. A liquid crystal display device according to claim 7, wherein said
black mask is composed of a polyimide resin material in which are mixed
metal oxide particles as a black coloring agent.
12. A liquid crystal display device according to claim 8, wherein said
black mask is composed of a polyimide resin material in which are mixed
metal oxide particles as a black coloring agent.
13. A liquid crystal display device according to claim 1, wherein said
black mask has a resistivity of at least 3.times.10.sup.6
.OMEGA..multidot.cm.
14. A liquid crystal display device according to claim 1, wherein
N.gtoreq.11.
15. A liquid crystal display device according to claim 1, wherein
M.gtoreq.7.
16. A liquid crystal display device according to claim 1, wherein said
first group of electrodes are electrically connected to each other, said
second group of electrodes are electrically connected to each other, and
one of said first group of electrodes and said second group of electrodes
is connected to a thin film transistor formed on one of said pair of
substrates.
17. A liquid crystal display device according to claim 1, wherein said
opening of said black mask is formed with respect to a pixel of the liquid
crystal display device.
18. A liquid crystal display device comprising:
a pair of substrates at least one of which is transparent;
a black mask formed on one of said pair of substrates and having an opening
which has at least one pair of edges confronting each other and extending
in a first direction;
a first group of electrodes and a second group of electrodes being formed
on at least one of said pair of substrates, extending in the first
direction of said one pair of edges of said opening of said black mask and
one of said first group of electrodes being disposed alternately with one
of said second group of electrodes;
a liquid crystal layer comprising a liquid crystal composition substance
having a dielectric anisotropy and held between said pair of substrates;
and
an orientation control film formed between said liquid crystal layer and
one of said pair of substrates for orienting liquid crystal molecules of
said liquid crystal composition substance in a predetermined direction;
at least one of said first group of electrodes and at least one of said
second group of electrodes are spaced from each other so as to divide a
region enclosed by said opening of said black mask into a pair of first
regions and at least one second region and to generate an electric field
having a component predominantly in parallel with the interface between
said orientation control film and said liquid crystal layer in each of
said pair of first regions and said at least one second region, said pair
of first regions and said at least one second region extending in the
first direction of said one pair of edges of said opening of said black
mask;
one of said pair of first regions being disposed adjacent to one of said
one pair of edges of said opening of said black mask and another of said
pair of first regions being disposed adjacent to another of said one pair
of edges of said opening of said black mask;
said at least one second region being spaced from both of said one pair of
edges of said opening of said black mask by each of said of first regions,
respectively,
said black mask has a resistivity of not smaller than 10.sup.M
.OMEGA..multidot.cm, and
wherein M is an integer satisfying the relationship of M.gtoreq.6.
19. A liquid crystal display device according to claim 18, wherein both of
said first group of electrodes and said second group of electrodes are
formed on another of said pair of substrates opposite to said one of said
pair of substrates on which said black mask is formed.
20. A liquid crystal display device according to claim 19, wherein two of
said first group of electrodes and said second group of electrodes
confront entirely with said black mask, and each electrode of said first
group of electrodes and said second group of electrodes other than the two
thereof has a region not confronting with said black mask.
21. A liquid crystal display device according to claim 18, wherein said
liquid crystal composition substance has a resistivity of not smaller than
10.sup.N .OMEGA..multidot.cm, and N is a integer satisfying the
relationship of N.gtoreq.9.
22. A liquid crystal display device according to claim 18, wherein said
first group of electrodes consists of three electrodes and said second
group of electrodes consists of two electrodes, respectively.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and,
particularly, to an active matrix liquid crystal display device of a high
picture quality with wide viewing angle characteristics comprising high
resistivity black matrix and with excellent light-shielding ability.
2. Description of the Prior Art
Display devices using a liquid crystal display device having reduced
thickness and reduced weight and consuming decreased amounts of electric
power have in recent years been widely used for personal computers, word
processors and other information equipment.
Basically, the liquid crystal display device has a matrix made up of a
number of electrodes arranged horizontally and vertically and a liquid
crystal layer interposed between the horizontal electrodes and the
vertical electrodes, and pixels are formed at the portions where two
electrodes intersect each other to display a two-dimensional picture.
The liquid crystal display devices of this kind can be divided into those
of a so-called passive matrix system which selects a predetermined pixel
at a timing of a pulse applied to horizontal and vertical electrodes, and
those of a so-called active matrix system in which a nonlinear element
such as transistor or the like is provided in each pixel and a
predetermined nonlinear element is selected.
In a liquid crystal display device of the active matrix system, non-linear
elements (switching elements) are provided at positions corresponding to a
plurality of pixel electrodes arranged in the form of a matrix.
Theoretically, the liquid crystal in each pixel is driven at all times
(duty ratio of 1.0). Compared with the so-called passive matrix system
employing a time-division multiplex driving system, therefore, the active
matrix system exhibits a good contrast and has been establishing a
technique that is indispensable particularly in the color liquid crystal
display devices. Thin-film transistors (TFTs) are representative examples
of the switching elements.
In a conventional thin-film transistor liquid crystal display element,
transparent electrodes are so formed as to face each other on the
interface of two substrates to drive the liquid crystal layer.
That is, there has been employed a display system as represented by a
so-called twisted nematic display system in which the direction of the
electric field applied to the liquid crystals is almost perpendicular to
the interface of the substrates owing to the employment of the
above-mentioned electrode structure.
As a system in which the direction of an electric field applied to the
liquid crystals is almost in parallel with the interface of the
substrates, furthermore, there has been proposed a system (so-called an
inplane electric field system) employing a pair of comb-toothed electrodes
formed on the surface of at least one of the substrates for driving the
liquid crystal layer as disclosed in, for example, Japanese Patent
Publication No. 21907/1988 and Japanese Patent Laid-Open No. 36058/1995.
The method of setting comb-toothed electrodes and the method of its
fabrication have been proposed already by the present applicant in
Japanese Patent Application No. 105862/1995.
In such an electrode structure, the major axes of molecules of the liquid
crystal layer (hereinafter also referred to simply as liquid crystal
molecules) are substantially in parallel with the surfaces of the
substrates, and the liquid crystal molecules are suppressed from being
erected in a direction perpendicular to the substrates. Therefore, the
brightness changes little even when the viewing angle is changed; i.e.,
the so-called viewing angle dependence does not almost exist, and wide
viewing angle characteristics are accomplished compared with those of the
vertical electric field system.
In a conventional black mask interposed among the colored layers of various
colors and constituting the substrate (color-filter substrate) of a color
filter, furthermore, a pattern of thin film of metal chromium or
low-reflection metal chromium has been formed. Or, a pattern of a thin
layer of a photosensitive resin has been formed, dispersing a black
coloring agent, or black carbon powder (chiefly graphite) therein, and
adding various pigments thereto.
The colored layers of the color-filter substrate usually have a structure
in which a protective layer PSV2 is formed on the colored layers FIL(R),
FIL(G), FIL (B) of which the pattern regions are separated like a mosaic
or vertical stripes for each of the pixels or colors.
When the colored layers are fabricated by using pigment-dispersed resin
materials in the color filter used for the active matrix-type liquid
crystal display devices, furthermore, the protective layer PSV2 is not
often employed.
FIG. 13 is a schematic sectional view illustrating the constitution of a
pixel that constitutes an inplane electric field-type liquid crystal
display device and illustrating the turn-on operation, wherein reference
numeral 1 denotes a TFT substrate, 1' denotes a color-filter substrate, 2
denotes a common electrode, 6 denotes an insulating film, 11 denotes pixel
electrodes, 12 denotes a protective film, 17 denotes a black mask, and 18
denotes a color filter.
In FIG. 13, a liquid crystal layer is held between the TFT substrate 1 and
the color filter substrate 1'. On the surfaces of the protective film 12
and of the color filter 18 are formed orientation films for establishing
the initial orientation of liquid crystal molecules of the liquid crystal
layer. Moreover, though not shown in FIG. 13, polarizer plates are
installed on the outer surface sides of the TFT substrate 1 and the color
filter substrate 1'.
In the above mentioned inplane electric field liquid crystal display
device, the pixel electrodes 11 and the common electrode 2 are formed on
one substrate (TFT substrate 1), and on the other substrate (color-filter
substrate 1') is formed a color filter 18 that constitutes a color of a
pixel demarcated by the black mask 17.
The black mask 17 demarcating the color filter prevents the reflection of
external light and enhances the contrast by absorbing light from the
neighboring pixels.
SUMMARY OF THE INVENTION
In a conventional vertical electric field liquid crystal display device
having a common electrode formed on the side of the color-filter
substrate, the black mask constituting the color-filter substrate is
required to have a high light absorption factor and a low light reflection
factor. However, no consideration concerning the resistivity of the black
mask has been taken.
That is, in the above-mentioned black mask using a resin material, a large
amount of graphite is added particularly to improve the absorption factor.
Therefore, the resistivity decreases with an increase in the amount of
graphite added. When metal chromium is used for the black mask,
furthermore, the light-shielding ability is improved greatly and the
resistivity becomes very small.
In the inplane electric field-type liquid crystal display device in which
the black mask has a small resistivity, however, the lines of electric
force from the pixel electrodes 11 are attracted by the black mask 17
having a small resistivity, as shown in FIG. 13, when a voltage is applied
between the pixel electrodes 11 and the common electrode 2 to turn the
pixel on, and the pattern of electric field is disturbed and tilted with
respect to the interface of the substrates. As a result, the horizontal
component of the lines of electric force is weakened, and a desired light
transmission factor is not obtained. Alternatively, so-called domains
occur at positions of the pixel electrodes 11 and the common electrode 2.
Accordingly, the contrast is degraded, color display becomes nonuniform,
and a good picture quality is not obtained.
FIGS. 14A and 14B are schematic diagrams illustrating a pixel in an inplane
electric field liquid crystal display device having two comb-toothed
common electrodes arranged in a pixel. FIG. 14A is a plan view and FIG.
14B is a sectional view cut along the line 14B--14B in FIG. 14A. A color
filter is formed on a portion surrounded by the black mask 17, and various
films are formed thereon and on the common electrodes 2 and on the pixel
electrodes 11, which, however, are not shown here.
In FIGS. 14A and 14B, a pixel is formed in an open region surrounded by the
black mask, a pixel electrode 11 and a common electrode 2 are arranged in
this region, and a liquid crystal layer is held between the TFT substrate
1 and the color filter substrate 1'. The black mask has a resistivity of
not larger than 10.sup.4 .OMEGA..multidot.cm.
By a signal voltage applied for turn on, an electric field is generated
between the common electrode 2 and the neighboring pixel electrode 11.
This electric field acts strongly upon the liquid crystal molecules
depending upon the magnitude of the applied signal voltage, whereby the
orientation of liquid crystal molecules rotates and light passes from the
TFT substrate 1 to the color-filter substrate 1' at an increased
transmission factor.
FIG. 15 is a diagram illustrating the transmission factor that varies
depending upon the position in the gap between the common electrode 2 and
the pixel electrode 11 shown in FIG. 14A, wherein a spot a denotes a
position away from the black mask 17 and a spot b denotes a position close
to the black mask 17.
As shown, the transmission factor increases with an increase in the signal
voltage applied between the common electrode 2 and the pixel electrode 11.
As shown in FIG. 14A, however, since the spot b is located close to the
black mask 17, the electric field pattern is formed at a sharp angle with
respect to the surface of the substrate. Accordingly, in a change in the
transmission factor with an increase in the voltage, the rise is behind
that of the spot a. In FIG. 15, the voltage of the spot b must be
increased by about one volt with respect to the spot a to obtain the same
transmission factor.
When the same voltage is applied, therefore, the transmission factor
differs between the central portion and the peripheral portion in a pixel,
and the color becomes nonuniform.
The object of the present invention is to provide a liquid crystal display
device of a so-called inplane electric field device having an improved
light-shielding ability, suppressing disturbance of the pattern of
electric field, and displaying a picture of high quality without
nonuniformity in color.
In order to accomplish the above-mentioned object, means 1 is characterized
in that, a liquid crystal display device comprises a black mask formed on
one of a pair of substrates at least one of which is transparent, a group
of electrodes formed on at least one of the pair of substrates, a liquid
crystal layer comprising a liquid crystal composition substance having a
dielectric anisotropy and held between the pair of substrates, an
orientation control film formed between the liquid crystal layer and one
of the substrates for orienting the liquid crystal molecules of the liquid
crystal composition substance in a predetermined direction, a polarizing
means laminated on at least one of the pair of substrates, and a drive
means for applying a drive voltage to the group of electrodes, wherein the
group of electrodes has a structure that the electrodes are so arranged as
to generate an electric field having a component predominantly in parallel
with the interface between the orientation control film and the liquid
crystal layer, said liquid crystal composition substance has a resistivity
of not smaller than 10.sup.N .OMEGA..multidot.cm, and said black mask has
a resistivity of not smaller than 10.sup.M .OMEGA..multidot.cm, wherein N
and M are integers satisfying the relationships N.gtoreq.9 and M.gtoreq.6.
Means 2 is characterized in that a liquid crystal display device comprises
a black mask formed on one of a pair of substrates at least one of which
is transparent, a group of electrodes formed on at least one of the pair
of substrates, a liquid crystal layer comprising a liquid crystal
composition substance having a dielectric anisotropy and held between the
pair of substrates, an orientation control film formed between the liquid
crystal layer and one of the substrates for orienting the liquid crystal
molecules of the liquid crystal composition substance in a predetermined
direction, a polarizing means laminated on at least one of the pair of
substrates, and a drive means for applying a drive voltage to the group of
electrodes, wherein the group of electrodes has a structure that the
electrodes are so arranged as to generate an electric field having a
component predominantly in parallel with the interface between the
orientation control film and the liquid crystal layer, said liquid crystal
composition substance has a resistivity of not smaller than 10.sup.N
.OMEGA..multidot.cm, and said black mask has a resistivity of not smaller
than 10.sup.M .OMEGA..multidot.cm, wherein N and M are integers satisfying
the relationships N.gtoreq.13 and M.gtoreq.7.
Means 3, according to means 1 or 2, is characterized in that metal oxide
particles are contained in the black mask.
Means 4, according to means 3, is characterized in that metal oxide
particles are particles of at least one of cobalt oxide, chromium oxide,
manganese oxide and nickel oxide.
Means 5, according to means 3, is characterized in that either or both of
an organic pigment and a graphite powder are contained in the black mask
in addition to the metal oxide particles.
Means 6, according to means 4, is characterized in that the cobalt oxide
particles are chiefly tricobalt tetroxide particles.
Means 7, according to means 4, is characterized in that any one of chromium
oxide, manganese oxide and nickel oxide is contained in addition to the
cobalt oxide.
Means 8, according to means 1 or 2, is characterized in that the black mask
contains the polyimide resin as a base material.
Means 9, according to means 8, is characterized in that the base material
of the black mask is a resin material having a polyimide group, the
composition of the resin material contains a component that is cured by
light and a component that is cured by heat, and the optical density
increases as the resin material is cured by heat. Means 10, according to
means 8 or 9, is characterized in that the black mask is composed of a
polyimide resin material which contains at least one or more kinds of
black coloring agents and other coloring agents different from the black
coloring agents.
Furthermore, means 11, according to means 8 or 9, is characterized in that
the black mask is composed of a polyimide resin material in which metal
oxide particles are mixed as a black coloring agent.
In the constitution of the above-mentioned means 1, the black matrix formed
on one of the pair of substrates shuts off the entry of light from the
neighboring pixels that are turned on, contributing to increasing the
contrast of a display image.
The group of electrodes formed on one or both of the pair of substrates
comprise a common electrode and a pixel electrode, and forms an electric
field pattern between the two electrodes when the pixel is turned on to
rotate the orientation of liquid crystal molecules of a liquid crystal
composition substance that constitutes the liquid crystal layer, so that
the light transmission factor changes. The orientation control film
(orientation film) works to orient the liquid crystal molecule of the
liquid crystal composition substance in a predetermined direction when no
electric field is applied.
The polarizing means is laminated on at least one of the pair of
substrates, and permits the passage of light that is polarized in a
specific direction before entering into the liquid crystal layer or after
having passed through the liquid crystal layer.
The drive means applies a drive voltage to the group of electrodes to turn
a predetermined pixel on to display an image.
The group of electrodes has a structure that the electrodes are so arranged
as to generate an electric field having a component predominantly in
parallel with the interface between the orientation control layer and the
liquid crystal layer. When the electric field is generated between the
common electrode and the pixel electrode constituting the group of
electrodes, the liquid crystal molecules are rotated in a plane
substantially in parallel with the interface.
The liquid crystal composition substance has a resistivity of not smaller
than 10.sup.N .OMEGA..multidot.cm and the black mask has a resistivity of
not smaller than 10.sup.M .OMEGA..multidot.cm (where N and M are integers)
satisfying the relationships N.gtoreq.9 and M.gtoreq.6, thereby to
effectively generate an electric field component in parallel with the
substrates.
Accordingly, the liquid crystal molecules rotate in a plane substantially
in parallel with the interface, making it possible to suppress the
occurrence of so-called domains and the rise of the drive voltage.
In the constitution of means 2, furthermore, the liquid crystal composition
substance has a resistivity of not smaller than 10.sup.N
.OMEGA..multidot.cm and the black mask has a resistivity of not smaller
than 10.sup.M .OMEGA..multidot.cm (where N and M are integers) satisfying
relationships N.gtoreq.13 and M.gtoreq.7, thereby to more effectively
generate an electric field component in parallel with the substrates than
that of means 1.
Accordingly, the liquid crystal molecules rotate in a plane substantially
in parallel with the interface, making it possible to further suppress the
occurrence of so-called domains and the rise of the drive voltage.
In the constitution of means 3, furthermore, metal oxide particles are
contained in the black mask formed on one of the pair of substrates at
least one of which is transparent. Therefore, the black mask exhibits an
increased resistivity yet maintaining an optical density, and the electric
field component is more effectively generated between the electrodes in a
plane nearly in parallel with the above-mentioned interface.
Accordingly, the liquid crystal molecules rotate in a plane nearly in
parallel with the interface, making it possible to suppress the occurrence
of so-called domains and the rise in the drive voltage, and enabling the
light transmission factor to be improved.
In the constitution of means 4, furthermore, the black mask contains cobalt
oxide particles, chromium oxide particles, manganese oxide particles or
nickel oxide particles so as to possess an increased optical density and
an increased resistivity. Therefore, the electric field component is
generated more effectively between the electrodes in a plane in parallel
with the above-mentioned interface.
Accordingly, the liquid crystal molecules rotate in a plane nearly in
parallel with the interface, making it possible to suppress the occurrence
of so-called domains and the rise of the drive voltage, and enabling the
light transmission factor to be improved.
In the constitution of means 5, the black mask contains either or both of
an organic pigment and a graphite powder in addition to the metal oxide
particles so as to possess an increased resistivity and to absorb light
more efficiently. Accordingly, the liquid crystal molecules rotate in a
plane nearly in parallel with the interface, making it possible to
suppress the occurrence of so-called domains and the rise of the drive
voltage, and enabling the light transmission factor to be improved.
In the constitution of means 6, tricobalt tetroxide is chiefly used as the
cobalt oxide particles so that the black mask maintains the resistivity
and the absorbency.
In the constitution of means 7, any one of chromium oxide, manganese oxide
or nickel oxide is contained in addition to the cobalt oxide, so that the
black mask maintains the resistivity and the light absorption factor.
In means 8 to 10, use is made of a polyimide photosensitive resin, and a
feature that the optical density increases in the step of curing the resin
by light and heat is utilized in order to obtain a black mask of nearly a
black color having a high insulating property.
That is, in the constitution of means 8, the black mask is comprised of a
material which contains a polyimide resin as the base material and has a
high resistivity. Therefore, the insulating property is prevented from
decreasing, and the electric field component for rotating the liquid
crystal molecules is effectively generated in parallel with the interface.
In the constitution of means 9, the black mask is made of a resin material
having a polyimide group and containing a component that is cured by light
and a component that is cured by heat. Therefore, there is formed a black
mask that is colored in black upon the curing by heat, and exhibits a
great light-shielding ability.
In the constitution of means 10, the black mask is made of the polyimide
resin material that contains at least one or more kinds of black coloring
agents and other coloring agents than the above-mentioned black coloring
agents. Therefore, the black mask exhibits a great light-shielding
ability.
In the constitution of means 11, the black mask is made of the polyimide
resin material in which is mixed metal oxide particles as a black coloring
agent. Therefore, the black mask exhibits a high resistivity and a great
light-shielding ability.
The above-mentioned polyimide-type photosensitive resin has in the molecule
skeleton thereof a functional group that absorbs visible rays but does not
contain carbon or graphite which has been conventionally contained. It is
therefore possible to set a low transmission factor without lowering the
resistivity.
The foregoing and other objects, advantages, manner of operation and novel
features of the present invention will be understood from the following
detailed description when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A to 1D are schematic diagrams of a pixel for explaining the
operation of an inplane electric field-type liquid crystal display device;
FIGS. 2A to 2C are diagrams illustrating a structure of a TFT substrate
constituting an embodiment of an inplane electric field liquid crystal
display device;
FIG. 3 is a diagram illustrating example 1 or 2 of the structure of a
color-filter substrate in the inplane electric field liquid crystal
display device;
FIG. 4 is a schematic diagram of an electric field pattern in a pixel in
cross section constituting the embodiment 1 or 2 of the inplane electric
field liquid crystal display device;
FIG. 5 is a diagram illustrating a rise of the drive voltage relative to
the resistivity of the black mask of when the resistivity of the liquid
crystal layer of the inplane electric field liquid crystal display device
is changed;
FIG. 6 is a diagram illustrating a change in the resistivity of the black
mask relative to the content of carbon therein and a change in the optical
density of when the film thickness is 1 .mu.m, in the embodiment 1 of the
present invention;
FIG. 7 is a sectional view illustrating an essential portion of the
color-filter substrate used in the embodiment 3 of the inplane electric
field color liquid crystal display device;
FIG. 8 is a diagram schematically illustrating the steps of forming the
black mask shown in FIG. 7;
FIG. 9 is a diagram illustrating the steps of fabricating the color-filter
substrate shown in FIG. 7;
FIG. 10 is a diagram showing the connection of an equivalent circuit of a
display matrix unit and the peripheral circuits in a liquid crystal
display device;
FIG. 11 is an exploded perspective view illustrating an example of the
constitution of the liquid crystal display device according to the present
invention;
FIG. 12 is a diagram showing the appearance of a personal computer for
explaining an information processing device in which a liquid crystal
display device of the present invention is mounted;
FIG. 13 is a sectional view for schematically illustrating the constitution
of a pixel constituting an inplane electric field liquid crystal display
device and for illustrating the turn-on operation;
FIGS. 14A and 14B are schematic diagrams of a pixel in an inplane electric
field liquid crystal display device in which two comb-toothed common
electrodes are arranged in a pixel; and
FIG. 15 is a diagram illustrating a change in the transmission factor
depending upon the position in the gap between the pixel electrode and the
common electrode shown in FIGS. 14A and 14B.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will now be described in detail with
reference to the drawings.
FIGS. 1A to 1D are schematic diagrams of a pixel for explaining the
operation of a liquid crystal display device to which the present
invention is applied. FIG. 1A is a sectional view of when no voltage is
applied, FIG. 1B is a sectional view of when a voltage is applied, FIG. 1C
is a plan view of when no voltage is applied, and FIG. 1D is a plan view
of when a voltage is applied. The voltage referred to here is a selection
voltage applied between the common electrode and the pixel electrode.
In FIGS. 1A and 1B, reference numerals 1 and 1' denote transparent glass
substrates (hereinafter also referred to simply as substrates), 2 denotes
a common electrode, 6 denotes an insulating film, 10 denotes a signal
wiring, 11 denotes a pixel electrode, 12 denotes a protective film, 13 and
13' denote polarizer plates, 14 and 14' denote axes of polarization of the
polarizer plates, 15 denotes the orientation of liquid crystal molecules,
16 denotes the direction of an electric field, 17 denotes a black mask
(BM), 18 denotes a color filter, 19 denotes a protective film (flattening
film), 20 and 20' denote orientation films, and reference numeral 21
denotes liquid crystal molecules (chiefly rod-like liquid crystal
molecules).
The liquid crystal display device comprises the polarizer plate 13', black
mask 17 for shielding light, color filter 18, protective film 19 and
orientation film 20' that are formed on one substrate (color-filter
substrate 1') of two transparent glass substrates 1 and 1'. On the other
substrate (TFT substrate) 1 via the liquid crystal 21 are formed the
polarizer plate 13, orientation film 20, signal electrode 10, pixel
electrode 11, common electrode 2, wirings and thin-film transistor (TFT).
FIGS. 1A and 1B do not illustrate wirings or thin-film transistors.
Referring to FIGS. 1A and 1C, the liquid crystal molecules 21 are oriented
homogeneously by the orientation films 20, 20' in the direction 15 of
orientation which is nearly in parallel with the planes of the substrates
1, 1'. In this state, the direction of initial orientation of liquid
crystal molecules 21 is nearly in agreement with the axis 14 of
polarization of the polarizer plate 13, and the axis 14' of polarization
of the upper polarizer plate 13' is perpendicular thereto and the pixel is
in a non-display (turned-off) state.
Referring next to FIGS. 1B and 1D, the voltage is applied between the
common electrode 2 and the pixel electrode 11 formed on the substrate 1 to
form an electric field (the direction 16 of electric field) in a direction
nearly in parallel with the interface of the substrates 1, 1'. Then, the
liquid crystal molecules 21 are oriented and rotated in a plane nearly in
parallel with the interface of the substrates 1, 1'. Accordingly, the
pixel is placed in a display (turned-on) state. A large number of pixels
are arranged to constitute a display device.
FIGS. 2A to 2C are diagrams illustrating the structure of a TFT substrate
which constitutes a liquid crystal display device of an embodiment of the
present invention, wherein FIG. 2A is a plan view, FIG. 2B is a sectional
view taken along the line 2B--2B of FIG. 2A, and FIG. 2C is a sectional
view taken along the line 2C--2C of FIG. 2A.
In FIGS. 2A to 2C, the same reference numerals as those of FIGS. 1A to 1D
denote the same portions, reference numeral 3 denotes a common wiring, 4
denotes a scanning electrode, 5 denotes a scanning wiring, 6 denotes an
insulating film, 7 denotes a semiconductor layer, 8 denotes a thin-film
transistor portion (TFT portion), 10 denotes a signal wiring, 11 denotes
pixel electrodes, and 12 denotes a protective film.
The scanning electrode 4, scanning wiring 5, common electrodes 2 and common
wiring 3 are provided in the same layer and are made of the same material.
The semiconductor layer 7 is formed via the thin layer and the insulating
film 6, and the signal wiring 10 and the pixel electrode 11 are formed in
the same layer using the same material.
Part of the pixel electrode 11 is so arranged as to overlap with the common
wiring 3 in a direction perpendicular to the surface of the substrate via
the insulating film 6, creating a capacitance to hold a signal voltage
that is applied between the pixel electrode 11 and the common electrode 2.
FIG. 3 is a diagram illustrating an example of the structure of the
color-filter substrate constituting the liquid crystal display device
according of the embodiment 1 of the present invention, wherein the same
reference numerals as those of FIGS. 1A to 1D denote the same portions.
As shown in FIG. 3, the color filter substrate has a plurality of color
filters (R G. B) demarcated by the black mask 17 on one surface of the
transparent substrate 1', and further has the protective film (smoothing
layer) 19 and the orientation film 20' formed thereon. The polarizer plate
13' is deposited on the other surface of the transparent substrate 1'.
When the liquid crystal layer has a resistivity of not smaller than
10.sup.N .OMEGA..multidot.cm, the black mask 17 demarcating a plurality of
color filters R, G and B must have a resistivity of not smaller than
10.sup.M .OMEGA..multidot.cm, satisfying the relationships N.gtoreq.9 and
M.gtoreq.6, where N and M are integers.
When the liquid crystal layer and the black mask have such resistivities,
the electric field pattern formed by the selection voltage applied between
the common electrode and the pixel electrode has an effectively increased
component nearly in parallel with the interface between the liquid crystal
layer and the orientation film, and makes it possible to suppress the rise
of the drive voltage. Furthermore, occurrence of domains is greatly
decreased, and high-contrast display is obtained.
FIG. 4 is a sectional view schematically illustrating an electric field
pattern of a pixel that constitutes the liquid crystal display device of
the embodiment 1 according to the present invention, wherein the lines of
electric force generated between the common electrode 2 and the pixel
electrodes 11 are not affected by the black mask 17, the electric field
pattern is nearly in parallel with the interface between the liquid
crystal layer and the orientation film, occurrence of domains is greatly
decreased at the positions of the pixel electrodes 11 and at the position
of the common electrodes 2, the transmission factor is enhanced in the
open region of the pixel, and a high-contrast display is obtained.
The same effects are produced even when the liquid crystal layer has a
resistivity of not smaller than 10.sup.N .OMEGA..multidot.cm and the black
mask has a resistivity of not smaller than 10.sup.M .OMEGA..multidot.cm (N
and M are integers), satisfying the relationships N.gtoreq.13 and
M.gtoreq.7.
In embodiment 1, the material of the black mask is blended with a mixture
of an organic pigment and carbon; i.e., the amount of carbon is adjusted
so that the above-mentioned desired resistivity is obtained.
FIG. 5 is a diagram illustrating the drive voltage relative to the
resistivity of the black mask of when the resistivities of the liquid
crystal layer and of the black mask of the aforementioned embodiment 1 are
changed.
In FIG. 5, assuming that the allowable value of drive voltage increase
relative to the allowable value of transmissivity change, which should be
less than one gray scale level, is not larger than 0.1 volt, the
resistivity of the black mask must be higher than 3.times.10.sup.6
.OMEGA..multidot.cm when the liquid crystal has a resistivity of 10.sup.9
.OMEGA..multidot.cm, and the resistivity of the black mask must be higher
than 5.times.10.sup.7 .OMEGA..multidot.cm when the liquid crystal has a
resistivity of 10.sup.13 .OMEGA..multidot.cm.
From these facts, the aforementioned effects are obtained by determining
the values M and N satisfying the relationships N.gtoreq.9 and M.gtoreq.6
or N.gtoreq.13 and M.gtoreq.7.
When the black mask contains carbon, the resistivity decreases with an
increase in the amount of carbon that is contained and increases with a
decrease in the amount of carbon. An increase in the amount of carbon
results in an increase in the optical density (hereinafter referred to as
OD value). However, since carbon is electrically conductive, it decreases
the resistivity.
That is, the amount of carbon must be so set as to satisfy the
above-mentioned mutually conflicting requirements.
FIG. 6 is a diagram illustrating a relationship between the resistivity
change of the black mask depending upon the amount of carbon and the OD
value of the black mask of when the film thickness is 1 .mu.m, wherein
curve a represents the resistivity of the black mask, and curve b
represents the OD value.
In FIG. 6, the abscissa represents the amount of carbon (relative value) in
the black mask, the ordinate of the left side represents the resistivity
(.OMEGA..multidot.cm) of the black mask and the ordinate of the right side
represents the OD value of when the film thickness is 1 .mu.m.
From the relationship between the resistivity that varies depending upon
the amount of carbon and the optical density (OD value) shown in FIG. 6,
it is understood that the resistivity of the black mask becomes not
smaller than 10.sup.6 .OMEGA..multidot.cm when the relative amount of
carbon is about 50, and the OD value can be determined to be more than 1.6
which is practically satisfactory.
As described earlier, the material of the black mask contains a mixture of
organic pigment and carbon, and the mixing ratio of carbon is adjusted to
accomplish the resistivity that lies within the above-mentioned range. The
present invention, however, is in no way limited thereto only but a
desired resistivity can be accomplished by using other light-absorbing
materials.
That is, in another embodiment 2 as shown in FIG. 3, the black mask 17
demarcating a plurality of color filters R, G, B can be formed by a known
lithographic method by using a resist that contains particles of a
tricobalt tetroxide (CO.sub.3 O.sub.4) as particles of cobalt oxide.
It is further possible to use a resist that contains tricobalt tetroxide
and either or both of an organic pigment and carbon (chiefly graphite).
It is further possible to use a resist containing any one of chromium
oxide, manganese oxide and nickel oxide.
The mixing ratio of the components of the resist is so adjusted that the
black mask 17 has a resistivity of not smaller than 10.sup.6
.OMEGA..multidot.cm.
Since the metal oxide particles such as cobalt oxide particles are
contained in the black mask, the light absorption factor can be further
increased, maintaining a large resistivity of the black mask. Then, the
liquid crystal molecules rotate in a plane nearly in parallel with the
interface, making it possible to suppress the occurrence of so-called
domains and the rise of the drive voltage and enabling the light
transmission factor to be enhanced.
FIG. 7 is a sectional view illustrating an essential portion of the
color-filter substrate used in a further embodiment 3.
The color filters of FIG. 7 have the black mask BM made of a polyimide-type
resin and formed on the glass substrate SUB2; i.e., color filters (pixels)
FIL(R), FIL(G) and FIL(B) demarcated by the black mask BM are provided.
FIG. 8 is a diagram schematically illustrating the steps of forming the
black mask shown in FIG. 7, wherein PBM denotes a polyimide photosensitive
resin film, MSIC denotes a photomask for exposing the black mask, hv
denotes ultraviolet rays, and BM' denotes a black mask pattern.
The above-mentioned polyimide photosensitive resin is, for example, a
photosensitive polyimide resin Ddp-1120(s) (trade name) manufactured by
Nitto Denko Corp.
In FIG. 8, a glass substrate SUB2 that serves as a color-filter substrate
is prepared (step A), and a polyimide photosensitive resin film PBM is
uniformly applied onto the glass substrate SUB2 by a spin-coating method
(step B).
The polyimide photosensitive resin film PBM is prebaked at about 70.degree.
C. for about 15 minutes and is dried.
Next, ultraviolet rays hv are applied via a photomask MSK having openings
corresponding to the pattern of arrangement of black masks (step C). Here,
the energy for the exposure is about 500 mJ/cm.sup.2. Due to the exposure,
the portions irradiated with ultraviolet rays undergo the cross-linking
reaction and the resin is cured.
After the exposure, the polyimide photosensitive resin film PBM is
heat-treated in an oven at 180.degree. C. for 10 minutes or on a hot plate
180.degree. C. for two minutes. Due to the heat-treatment, the density of
the polyimide photosensitive resin film PBM increases and the film PBM
exhibits increased light-shielding ability.
After the heat-treatment, the polyimide photosensitive resin film PBM is
developed with a developing solution to remove the portions that are not
irradiated with ultraviolet rays, whereby a black mask pattern BM' made of
the polyimide resin is formed (step D).
Finally, the black mask pattern BM' is cured at 350.degree. C. to
400.degree. C. for about one hour to form the black mask BM (step E).
The processing conditions in the above-mentioned steps are merely examples
and can be changed depending upon the thickness of the film that is
applied and the blackness that is required.
The polyimide resin film is blackened by being cured by heat in the step of
heat-treatment after the exposure to light. The principle of blackening
has been disclosed in Omote Toshihiko, Hayashi Shunnichi, Fujii Hirobumi,
"Polymer Preprints, Japan", Vol. 41, No. 7, 1992, pp. 2836-2838.
As described earlier, the material constituting the black mask is the
polyimide resin not containing electrically conductive material.
Therefore, the black matrix exhibits a large resistance.
Then, the pixels (ROB) are formed. As required, furthermore, a flattening
film or a protective layer is formed thereon to obtain a color-filter
substrate.
In the inplane electric field liquid crystal element described earlier, the
opposing electrodes are not required on the side of the color-filter
substrate.
Next, a process for forming color filters of various colors on the
color-filter substrate having a black mask formed by the above-mentioned
processing will be described below.
FIG. 9 is a diagram illustrating the steps of producing the color-filter
substrate used for the color liquid crystal display device according to
the embodiment 3.
First, the black matrix is formed on the glass substrate, using the process
explained with reference to FIG. 8.
The pattern of the black mask serves as a reference of the whole
dimensional precision and for forming the color filters (pixels).
The thickness of the black mask is determined depending upon the optical
properties thereof, i.e., depending upon the light-shielding ability. In
the embodiment 3, the thickness of the black mask is about 1.0 to about
1.5 .mu.m.
A red pigment-dispersed resin material is applied by spin-coating or the
like method onto the substrate on which the black mask has been formed,
and is exposed to ultraviolet rays via an exposure mask having an opening
corresponding to the red filter. The material is developed to leave the
exposed portions, cured and dried by postbaking to form a red filter
FIL(R).
Next, a green pigment-dispersed resin material is applied by spin-coating
or the like method, and is exposed to ultraviolet rays via an exposure
mask having an opening corresponding to the green filter. The material is
developed to leave the exposed portions, cured and dried by postbaking to
form a green filter FIL(G).
Similarly, a blue pigment-dispersed resin material is applied by
spin-coating or the like method, and is exposed to ultraviolet rays via an
exposure mask having an opening corresponding to the blue filter. The
material is developed to leave the exposed portions, cured and dried by
postbaking to form a blue filter FIL(B).
Through these steps, color filters of three colors demarcated by the black
mask BM are formed.
According to the embodiment 3, the black mask formed among the pixels
exhibit a high light absorption factor, making it possible to provide a
color liquid crystal display device having an excellent contrast and a
high reliability.
In this embodiment, when the black mask has a resistivity of not smaller
than 10.sup.7 .OMEGA..multidot.cm, a coloring agent may be added to the
color-filter material to control the transmission factor.
The coloring agents to be added to the resin-type black mask material may
be graphite, carbon, red, green and blue pigments, or metal oxide
particles.
Among the above-mentioned coloring agents, pigments have little electrical
conductivity. Therefore, addition of the pigments makes it possible to
compensate for low absorption factor among the spectral characteristics of
the polyimide-type resin.
An increase in the amount of graphite or carbon to increase the
light-shielding ability results in an increase in the electric
conductivity. Therefore, limitation is imposed on the amount of their
addition.
The amount of addition, however, also varies depending upon the resistance
of the resin that is used, the resistance of the material that is added,
and the size (particle diameter).
In particular, graphite and carbon have high light-shielding ability and
are preferable for increasing the OD (optical density) value.
As the black coloring agent, furthermore, use is made of metal oxide
particles such as of the aforementioned cobalt oxide, chromium oxide,
manganese oxide or nickel oxide, thereby to form a black mask that
exhibits a high light absorption factor, a light-shielding ability and a
high resistivity.
According to the embodiment 3 as described above, the color-filter
substrate is fabricated by using the polyimide photosensitive resin to
provide a color liquid crystal surface having a high contrast.
A more specific constitution of the present invention will be described.
FIG. 10 is a diagram illustrating the connection of an equivalent circuit
of a display matrix unit in the liquid crystal display device of the
present invention and the peripheral circuits.
In FIG. 10, symbol AR denotes a matrix array in which a plurality of pixels
are two-dimensionally arranged, X denotes drain lines DL, and subscripts
G, B, R denote pixels of green blue and red colors.
Symbol DTM denotes drain terminals, GTM denotes gate terminals, Y denotes
gate lines GL, and subscripts 1, 2, 3, - - - , and are in the order of the
scanning timings. The gate lines Y (subscripts are omitted) are connected
to a gate driver unit V.
The drain lines X (subscripts are omitted) are connected to a drain driver
unit H arranged along one of the long sides of the display panel, and
terminals are led out from one side only of the liquid crystal display
panel like the gate lines Y.
SUP includes a power supply unit for obtaining stabilized voltages as basic
gray-scale levels whose voltages are generated by dividing the voltage of
a voltage supply, and a converter for converting information for the CRT
(cathode-ray tube) from a host (host arithmetic unit) into information for
the TFT liquid crystal display device.
FIG. 11 is an exploded perspective view illustrating the constitution of
the liquid crystal display device according to the present invention,
i.e., specifically illustrating the structure of the liquid crystal
display device (hereinafter referred to as module in which the liquid
crystal display panel, circuit board, backlight and other constituent
members are combined as a unitary structure: MDL).
In FIG. 11, symbol SHD denotes a shielded case (also referred to as a metal
frame) made of a metal plate, WD denotes a display window, INS1 to INS3
denote insulating sheets, PCB1 to PCB3 denote circuit boards (PCB1 is a
circuit board on the drain side or a circuit board for drain driver, PCB2
is a circuit board on the gate side, PCB3 is an interface circuit board),
JN1 to JN3 denote joiners for electrically connecting the circuit boards
PCB1 to PCB3 together, TCP1 and TCP2 denote tape carrier packages, PNL
denotes a liquid crystal display panel, GC denotes a rubber cushion, ILS
denotes a light-shielding spacer, PRS denotes a prism sheet, SPS denotes a
diffusion sheet, GLB denotes a light-guide plate, RFS denotes a reflection
sheet, MCA denotes a lower case (molded frame) formed by one-piece
molding, MO denotes an opening of the MCA, LP denotes a fluorescent lamp,
LPC denotes a lamp cable, GB denotes a rubber bush for supporting the
fluorescent lamp LP, BAT denotes a double-sided adhesive tape, and BL
denotes a backlight comprising a fluorescent lamp, a light-guide plate and
so on. Each part is stacked maintaining a relationship as shown thereby to
assemble the liquid crystal display module MDL.
The liquid crystal display module MDL has two kinds of
accommodating/holding members, i.e., a lower case MCA and a shielded case
SHD. The metallic shielded case SHD accommodating and holding the
insulating sheets INS1 to INS3, the circuit boards PCB1 to PCB3, and the
liquid crystal display panel PNL is joined to the lower case MCA holding
the backlight BL made up of the fluorescent lamp LP, the light-guide plate
GLB, the prism sheet PRS and so on.
On the circuit board PCB1 for drain driver is mounted an integrated circuit
chip for driving the pixels of the liquid crystal display panel PNL, and
on the interface circuit board PCB3 are mounted an integrated circuit chip
for receiving video signals from the external host and for receiving
control signals such as timing signals, and a timing converter TCON for
generating clock signals by processing timing signals.
The clock signals generated by the timing converter are fed to the
integrated circuit chip mounted on the circuit board PCB1 for drain driver
via a clock signal line CLL laid on the interface circuit board PCB3 and
on the circuit board PCB1 for drain driver.
The interface circuit board PCB3 and the circuit board PCB1 for drain
driver are multilayer wiring boards, and the clock signal line CLL is
formed as an inner-layer wiring in the interface circuit board PCB3 and in
the circuit board PCB1 for drain driver.
The circuit board PCB1 on the drain side for driving TFTS, the circuit
board PCB2 on the gate side and the interface circuit board PCB3 are
connected to the liquid crystal display panel PNL by tape carrier packages
TCP1, TCP2, and the circuit boards are connected together by joiners JN1,
JN2 and JN3.
The liquid crystal display panel PNL is an inplane electric field liquid
crystal display device of the present invention, and the black mask formed
on the color-filter substrate has a large resistivity so that an electric
field pattern is formed between a pixel electrode and a common electrode
almost in parallel with the interface of the liquid crystal layer.
FIG. 12 is a diagram showing the appearance of a personal computer for
explaining an information processing device having a liquid crystal
display device of the present invention, wherein IV denotes an inverter
power supply for driving a fluorescent lamp and CPU denotes a central
processing unit on the host side.
As shown in FIG. 12, the personal computer equipped with the liquid crystal
display device of the present invention has the circuit board for drain
driver (circuit board for horizontal driver: circuit board on the drain
side) PCB1 disposed at only the upper portion of the screen, leaving a
margin in space on the lower side (keyboard side) of the display unit.
Therefore, the space (hinge space) required to install hinges for coupling
the keyboard unit and the display unit together can be small. This makes
it possible to decrease the outer size of the display unit and, hence, to
reduce the size of the personal computer as a whole.
According to the present invention as described above, the electric field
created by the signal voltage in the so-called inplane electric field
liquid crystal display device does hardly interfere with the black mask.
Therefore, the electric field pattern formed by the selection voltage
applied between the common electrode and the pixel electrodes is nearly in
parallel with the interface between the liquid crystal layer and the
orientation film, making it possible to suppress the rise of the drive
voltage. Since the electric field pattern is not disturbed, the domains do
not occur, and the liquid crystal display device has a high picture
quality without nonuniformity in color.
The present invention is not limited to the liquid crystal display device
of the TFT-type only but can be applied to the liquid crystal display
devices of any other type inclusive of the active matrix type and the
so-called simple matrix type.
In this embodiment, furthermore, the black mask is formed on one substrate
side, and a group of electrodes are formed on the other substrate to
generate an electric field nearly in parallel with the substrates. They,
however, may be formed on the same substrate in compliance with the
present invention, as a matter of course.
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